Now there's another reason to get back to nature. A new study reveals that people who grow up in more rural environments are less likely to develop allergies. The reason may be that environments rich with species harbor more friendly microbes, which colonize our bodies and protect against inflammatory disorders.

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"We are proposing that contact of people, particularly children, with the natural environment and biodiversity could be really important for the development of the immune system," says Ilkka Hanski, an ecologist at the University of Helsinki and lead author of the study.

Hanski and his colleagues investigated the biodiversity hypothesis, or the assertion that the global decline in biodiversity and decreasing contact with it is linked to the escalating prevalence of chronic inflammatory and autoimmune diseases. To test whether or not biodiversity does indeed create a shield against such conditions, the team investigated the microbial diversity of 118 teenagers. The study participants, who had lived in the same houses their whole lives, were chosen at random from a 100-by-150-kilometer block in eastern Finland. Some kids lived on rural, isolated farms, while others lived in larger towns. The researchers controlled for factors such as whether family members smoked, if pets lived in the house, and what type of allergens the subjects were sensitive to ensure that correlation with the bacteria's health benefits wasn't driven by a single allergen.

The group then took microbial samples of an area on their subjects' forearms and sequenced the DNA to figure out which species of microbes were present. They also surveyed all of the types of plants growing around the adolescents' homes. The participants were part of a separate long-term allergy study, so the researchers took advantage of that data to investigate the connection between biodiversity and allergies.

Though individuals with allergies lived throughout the study area, the authors found that allergies were tied to the amount of biodiversity around the teenagers' homes; the more forest and agricultural land, the lower the prevalence of allergies. On the other hand, kids living near bodies of water or in urban centers had significantly higher levels of allergies.